Im not a plumber,,,,however i will suggest a solution,
You need to add water to the system as the pressure is down. Use the filling loop under the boiler to fill it. It should be filled until your boiler guage reads a 1 bar.
The filling loop will need to be connected to both screwed connections and the valve opened until the right pressure is reached ( 1 Bar)
Hope it helps
Paul
January 2009